When a device having a Josephson junction that is the base of a superconducting device is produced, it is necessary to precisely form a tunnel layer as a barrier. Superconducting coherence length at the interface of a tunnel layer and a superconductor is an important parameter to control to precisely form a tunnel layer in manufacturing a superconducting device.
Superconducting devices having Josephson junctions can be classified into two large groups: laminated type and flat type. Because the superconductive properties of an oxide superconductor that constitutes a superconducting device are sensitive to the crystal structure and composition, deteriorated layers may be produced due to defects at the junction interface. In such a case, if the coherence length is short, good junction properties cannot be obtained. In regard to a c-axis oriented thin film, which is widely used in laminated type devices, because the coherence length in the direction of the c-axis is short, forming a tunnel junction is difficult. Therefore there have been a reproducibility problems in the forming process.
Furthermore, in the field of superconducting devices, an integrated device is expected to achieve. In an integrated superconducting device, it is known that consistency among the properties of Josephson junctions affects the sensitivity of the device.
In view of the problems described above, research concerning reproducibility has been actively continued. In this respect, flat type devices using grain boundary junctions formed on a bicrystal substrate having one-dimensional grain boundary thereon have good reproducibility, and Josephson junctions can be formed relatively easily in this type of device. However, since the location to form a superconducting device is fixed in this type of device, there have been problems in the integrating process. Therefore, there have been problems in both laminated type devices and flat type devices for practical use.